1. Field of the Invention
The present invention relates generally to motion control systems providing real-time control of industrial servo motors. More particularly, the invention pertains to a motion control system and method for providing improved control and performance in a multi-axis servo motor system.
2. Description of the Prior Art
In industrial automation applications, motion control systems are often used to control servo motors of an industrial machine to provide for accurate and repeatable positioning of moving machine parts and workpieces.
Multi-axis motion occurs when two or more axes of motion are involved in a single machine. The need for multi-axis synchronization arises when the axes must move together and the relationship between their respective motion is important. The position and velocity relationship between the axes will often be significant to the proper operation of the machine. Position coordination during motion may be required, for example, to avoid a collision between a moving machine part and another object. Accordingly, where multiple axes control the orientation of a moving part, the position and velocity synchronization of the axes will determine how accurately the part is oriented as it moves.
A typical motion control system consists of a motor, motor drive, and a motion controller. The controller accepts motion commands from a host computer or an internally stored program These commands are interpreted by the controller to generate continuously updated position commands to the drive. The motor drive controls the current and frequency to the motor, which will result in the commanded position. In a multi-axis system, one controller can control several motors and drive combinations, or alternatively separate controllers can be operated under the control of a central control system
Electronic feedback systems are employed by the controller, either from an incremental encoder or from a resolver. The actual position and velocity of the motor derived from the feedback is compared with that commanded in the motion profile during the controlled operation.
In an asynchronous multi-axis control system, a series of moves are provided for each axis within a table. Each move typically includes a starting time, ending time, and a distance to be traveled. In operation, the moves for each axis will operate in an asynchronous fashion to one another.
Typical prior art motion control systems have a basic acceleration/steady-state/deceleration motion profile. During the steady-state velocity portion of the profile where the velocity is constant, the applied acceleration or force is equal to zero. When the applied force is zero, the only force remaining is due completely to mechanical compensation through a PID loop. In other words, the machine is operating in a random compensation mode, which has been found to prematurely wear the mechanical system.
As will be described in greater detail hereinafter, the method and apparatus of the present invention solves the aforementioned problems by substantially eliminating the steady-state velocity from a move and employs a number of novel features that render it highly advantageous over the prior art.